Making ifSecond parameter as optional on Task Option.MatchAsync

[vaclavpacholik]

Let's make the second parameter optional to avoid forcing developers to specify the second function that does nothing

e.g.:

await myOption.MatchAsync(async r =>
    {
        await something...
        //do something else
    },
    _ => Task.CompletedTask
);

=>

await myOption.MatchAsync(async r =>
{
    await something...
    //do something else
});

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